figure



May 12, 1964 w. MANTEUFFEL Re. 25,574

SOLID STATE POWER STAGE AMPLIFIER EMPLOYING SILICON RECTIFIERS ANDHALF-CYCLE RESPONSE MAGNETIC AMPLIFIERS Original Filed Feb. 12, I959co/vmm SIG/VAL STAGE L? Ffg. d 68, H958 (JR-[FIRES 3 080-3 r095;wear/195s Q, Q k ,g N N I TIME TIME I b: asfifififi 680- 17/758CSIP-ZF/RES a 2 cm 4/7195) x I 2 79, 4, E mean/95s N cow-.3 fl/PAS m J,,7 in Men to)": Q Erich W. Manteuffef, Q I x cs? lf'l/PZS by 4 Wx H/lsAt Orv-ray.

United States Patent Ofilice Matter enclosed in heavy brackets appearsin the original patent but forms no part of this reissue specification;matter printed in italics indicates the additions made by reissue.

This invention relates to power amplifiers of the type which provide anoutput signal of variable magnitude and polarity, and more particularlyto a solid-state power stage amplifier which exploits thecharacteristics of controlled silicon rectifiers.

Many of the prior art magnetic amplifiers used at the present time forproducing an output signal of variable magnitude and polarity requirethe use of power reactors. The weight and volume of such bulky powerreactors is highly undesirable where the use of the amplifier in anaircraft or like vehicle is contemplated. Moreover, in many of theseprior art amplifiers which provide two stages of amplification, separatebalancing of the individual stages is necessary. The internal lossesencountered in these prior art magnetic amplifiers are very appreciableif they are designed to function properly with a reasonable temperaturerise.

The present invention contemplates a new solid-state power stageamplifier capable of producing an output voltage of variable magnitudeand polarity for use by components such as two-phase servomotors.According to the inventive concept, the properties of the recentlydeveloped controlled silicon rectifier are exploited. Such rectifiersare capable of being gated conductive at any given instant during thealternating current cycle. To those skilled in the art, an analogybetween this property of controlled silicon rectifiers and conventionalgrid controlled thyratron tubes will immediately present itself. Thisanalogy is accurate, in that the controlled silicon rectifier doesactually comprise the solid-state counterpart of a conventional gridcontrolled gaseous conduction device. By employing this particularphenomenon of solid-state conduction, relatively large amounts of powercan be controlled. The use of such controlled silicon rectifiers has thevirtue of providing a magnetic amplifier with a physical size and weightwhich is negligible in comparison to the weight and size of aconventional magnetic amplifier having an equivalent power handlingcapacity. The internal losses associated with a circuit which utilizessuch rectifiers are practically negligible compared to the power losseswhich characterize either conventional thyratron or magnetic poweramplifiers designed for the same temperature rise and correspondingweight or volume.

In practicing the present invention, four controlled silicon rectifiersin a bridge type configuration are gated by small magnetic half-cycleresponse amplifiers. By utilizing a center tapped output transformer, anoutput signal of controllable magnitude and polarity is obtained bygating the control windings of the half-cycle response amplifiers withan AC. control signal of predetermined amplitude and polarity. Themagnetic amplifier thus provided yields a very large power gain atresponse times of one-half cycle of conventional supply frequency. Byusing the inventive amplifier for controlling an element such as atwo-phase servomotor, the need for bulky power reactors previouslyrequired in conventional known power amplifiers is completelyeliminated. It will thus Re. 25,574 Reissued May 12, 1964 be appreciatedthat both the weight and volume of the proposed system are.significantly less than that which characterizes prior art magneticamplifier type units. 9

Moreover, since the controlled rectifiers used in the present inventionfire in exact synchronism with the halfcycle response magneticamplifiers, the problem of separately balancing the individual stages ofthe two-stage magnetic amplifiers is entirely avoided. This is due inpart to the fact that the different signals in the power stage amplifierof the present invention are electrically isolated from each other.

Accordingly, therefore, a primary object of the present invention is toprovide a solid-state power stage amplifier which exploits theproperties of controlled silicon rectifiers for producing an outputpotential of variable magnitude and polarity.

Another object of the present invention is to teach a combination ofcircuitry and components in which halfcycle response magnetic amplifiersare used in conjunction with controlled silicon rectifiers for providingoutput signals of predetermined magnitude and polarity.

Still another object of the present invention is to provide method andmeans for accomplishing power amplification in which the bulky powerreactors of the prior art systems are eliminated with attendantelimination of balance problems, and in which substantial power gain athalf-cycle response is achieved.

A further object of this invention is to disclose a new bridge-typeamplifier circuit incorporating controlled silicon rectifiers which aregated conductive at an instant during the alternating current supplywave which is determined by the bias levelof a plurality of individualhalf-cycle magnetic amplifiers.

A further object of this invention is to provide bridgetype circuitryutilizing a number of controlled silicon rectifiers adapted toexperience conduction therethrough in response to the bias controlsetting of a plurality of saturable reactors connected to influence thecontrol electrodes of said rectifiers.

A still further object of the present invention is to teach a method andmeans for deriving a voltage of control lable magnitude and polarity inaccordance with the magnitude and polarity of a gating control signalwhich is supplied to a group of saturable reactors employed ininitiating conduction through a plurality of controlled siliconrectifiers.

These and other objects and advantages of the present invention willbecome apparent by referring to the accompanying detailed descriptionand drawings in which like numerals indicate like parts, and in which:

FIGURE 1 illustrates the circuitry and components of a bridge-typecircuit which uses controlled silicon rectifiers and magnetic half-cycleresponse amplifiers to provide a solid-state power stage amplifieraccording to the teachings of the present invention.

FIGURE 2 illustrates a wave form diagram of the conduction periods whichcharacterize the quiescent operating level of the power stage amplifier.

FIGURE 3 illustrates a wave form diagram of the conduction periods whichoccur when the saturable reactors are gated to: initiate conductionthrough the controlled silicon rectifiers at predetermined instants oftime.

FIGURE 4 shows a wave form of the conduction eriods and firing sequencewhich occurs when the polarity of the gating signals for the saturablereactors is reversed.

Turning now to the detailed description of the invention, and moreparticularly toFIGURE 1 of the accompanying drawings, the referencecharacters C-1 and C-2 have been used in this figure to identify a setof contacts which may be connected to a source of sinusoidal supplyvoltage of suitable amplitude and frequency. The contacts C-1 and C-2are connected to apply alternating current energy to a bridge circuitconfiguration having four connection points identified by the referenceletters A, B, C and D. Thus, the contact C-l is coupled to theconnection point B through a current limiting resistor RO2. This contactis also tied to the connection point A in the upper portion of thedrawing through a current limiting resistor R-Ol.

Directly beneath the connection point B in FIGURE 1, there isillustrated a transformer T1, which is provided with a center tappedprimary winding T-1P. This transformer is also equipped with a secondarywinding T-lS, and the secondary winding T1S is connected to supplyenergy to the control field of a conventional two-phase servomotor 12.The servomotor 12 is provided with the usual 'referencefield 14.

The servom'otor 12 is of conventional construction and design, and ischaracterized by the ability to rotate in either clockwise orcounterclockwise direction. The direction of rotation of the motor isgoverned by the polarity of the field current which is supplied to thecontrol fleld 10. In practicing the present invention, the direction ofcurrent flow through the control field 10 may be reversed byadjustingthe magnitude of the gating control'signals which are applied to thecontrol windings of a plurality of saturable reactors, in a "manner tobe explained more fully later in the present specification.

Returning now to the detailed description of FIGURE 1, it will beobserved that the contact (3-2 in the righthand portion of the drawingis conductively connected to the center tap of the primary winding T-IPof transformer T-1. In addition, one end of the primary winding T-IP istied directly to the connection point C for the bridge circuit shownimmediately thcreabove, while the opposite end of primary winding T1P isconnected to the connection point "D inthe right side of the bridgecircuit.

' The bridge-type circuit in FIGURE 1 will also be seen to include aplurality of controlled silicon rectifiers which have been identified bythe reference characters CSR-l, CSR2, CSR-3 and CSR4. The first of theserectifiers CSR1 is located between the connection points C and A and ispoled to conduct current whenpositive potential is applied to the anodeof the rectifier identified by the arrow symbol, and when positivepotential is applied .to the gate electrode of the unit with respect tothe cathode. The'flow of such current will, in the case of CSR-l, as inall other cases, be in the direction of the arrow;

Directly beneath the rectifier CSR-l, a controlled silicon rectifierCSR-2 is located between the connection points B and C, and is poled toconduct current in the direction indicated by the arrow symbol whenpositive voltage is applied to this element, and the gate electrode ofthe rectifier is gated to initiate conduction therethrough.

The controlled silicon rectifier CSR-S iscoupled between the connectionpoints D and A in FIGURE 1 and is poled to conduct current under properconditions in the direction indicated by the arrow symbol. In likemanner, the controlled silicon rectifier identified by the referencecharacter CSR-4 is tied between the connection points B and D and issimilarly poled when gated conductive to allow current flow in thedirection indicated by the arrow symbol.

Continuing with the detailed description of the invention, the referencecharacter T-2 has been used in FIGURE 1 to identify an auxiliarytransformer illustrated in the central portion of the drawing. Thistransformer is provided with a primary winding which is designated T-2Pand is also provided with a plurality of secondary windings identifiedgenerally by the designation T-ZS, with an appropriate subscriptappended to this designation. The several secondary windings of thetransformer T2 identified in this manner will be seen to include asecondary winding T-2S located in the upper portion of the drawing inproximity to connection point A. In the lower righ -hand central portionof the bridge circuit winding T-2P there is finally illustratedsecondary Winding "if-2S This winding is to be used for supplyingcurrent to the bias windings (not shown) of four saturable reactors tobe described next.

The power stage amplifier circuitry of the present invention alsoemploys a plurality of half-cycle response magnetic amplifiers, each ofwhich take the form of a saturable reactor equipped with a gate winding,a con-- trol winding for receiving a control current and a conventionalbias winding. In this patent specification, the terms saturable reactorand half-cycle response magnetic amplifier are frequently usedinterchangeably, and will be understood to mean the same thing. In orderto avoid needlessly complicating the drawing of the circuitry andcomponents in FIGURE 1, the bias windings for the several saturablereactors have not been illustrated.

The half-cycle response magnetic amplifiers, or saturab'le reactors asthey are referred to interchangeably in the present specification, areidentified in the power amplifier bridge circuit by the referencecharacters SR-l, SR-Z, SR3 and SR-d.

The location and interconnection details of these reactors is asfollows. In the upper left-hand corner of the bridge circuit, the gatewinding of the saturable reactor SR1 is connected in an individualseries circuit which includes a current ilimiting resistor R1, a silicondiode or like device D-1, and the gate and cathode terminals of thesilicon rectifier CSR-l. The series circuit for this gate winding alsoincludes the transformer winding T-ZS which, as will be recalled fromthe earlier portion of the specification, comprises one of the secondarywindings of the auxiliary transformer T-2. It will be observed that oneend of the secondary winding T-ZS is tied to the connection point A andtherefore to the cathode terminal of CSR shown immediately thereabove.

The saturable reactor SR2 is located in the lower left central portionof FIGURE 1 and will be seen to comprise one of a series of elementsconnected in an individual series circuit. This series circuit includesthe current limiting resistor R-2, the silicon diode or like device D-Z,the gate and cathode terminals of the silicon rectifier CSR-Z, and thesecondary winding T-2S In the upper right-hard portion of the bridgecircuit, the operating winding of the saturable reactor SIR-3 isconnected in an individual series circuitwhich includes a currentlimiting resistor R-3, a silicon diode or equivalent type device D3, thegate and cathode terminals of the silicon rectifier CSR3, and thesecondary winding T2S or" the auxiliary transformer T-Z.

Lastly, the operating winding of the saturable reactor SR-4 will be seento form one element in an individual series circuit illustrated in thelower right central portion of the bridge circuit in FIGURE 1. Moreparticularly, the saturable reactor SR4 is connected in series with acurrent limiting resistor R-4, a diode or equivalent element D4, thegate and cathode terminals of the silicon rectifier CSR4, and thesecondary winding IF-2S of the aturilialy transformer T-2.

In continuing the detailed description of the mode of connection of thesaturable reactors, reference to the means or providing control currentto the control windings of the several saturable reactors will now bemade. The control windings of the saturable reactors SR4 and SR3 in theupper portion of FIGURE 1 are connected in series with the controlwindings of saturable reactors SR-4 and SR2 depicted in the lowerportion of the bridge circuit. A winding T-lS disposed to receive energyby induction from the transformer T-l is also connected in series withthe control windings for the reactors SR-l, SR-Z, Sit-3 and ELF-- 5. Thecircuit which defines this series loop is connected to receive energyfrom a control signal stage 15 shown in the left-hand portion of theillustration. The control signal stage 15 may be of conventionalconstruction and detail, and is capable of providing an output signal ofvariable amplitude and polarity to the seriesconnected control windingsof the several saturable reactors. This output signal may be fixed, orrelatively constant, or may comprise a condition responsive potentialwhich alters .the amplitude and polarity of the output bridge poweravailable at the secondary winding of transformer T-l.

The winding T-1S shown in inductive proximity to the transformer T1serves to introduce a compensating voltage into the series circuit forthe control windings. This compensating voltage is proportional to theload voltage and is provided in order to eliminate influences on thewave shape of the control current from the gate currents of thesaturable reactors. The provision for the auxiliary winding T-1S in thismanner also has the effect of increasing the total amplificationafforded by the power stage amplifier of the present invention.

Having discussed the type of elements employed in the bridge circuit ofFIGURE 1, along with the specific mode of interconnecting such elements,the detailed description of the manner of operation of the bridge-typepower amplifier will now be provided. In readying the bridge circuit ofFIGURE 1 for operation, it is desirable to regulate the value of thebias current which flows through the bias windings (not shown) of thesaturable reactors in order to establish a quiescent operating point forthe power amplifier. By adjusting the value of this current in the biaswindings of the four reactors SR1, SR-Z, SR-3 and SR-4, the reactors areset to initiate conduction through the respective controlled siliconrectifiers at the 90 point on the sine wave of alternating currentsupply voltage. In setting this quiescent operating point, the reactorsSR-l and SR-3 are biased to initiate conduction at' 90 electricaldegrees during the positive half-cycle of potential. The reactors SR-2and SR4, on the other hand, eifect initiation of current flow throughthe associated controlled silicon rectifiers after 90 of thecorresponding negative half-cycle has elapsed. This value would ofcourse correspond to 270 measured from the time origin. As earliermentioned in the present patent specification, the bias windings for theseveral saturable reactors are of conventional construction and havebeen omitted from the drawing in FIGURE 1 for the purpose of clarity. IV

Proceeding with the explanation of the theory of operation, it should beappreciated that the four half-cycle magnetic amplifiers comprisingsaturable reactors SR-l through SR-4, the respective silicon diodes D1through D-4 and the current limiting resistors R-1 through R-4 serve toregulate the controlled silicon rectifiers CSR-l through CSR-4 bydetermining the instants of firing. The manner in which this is done,and the analogy to the operation of a grid-controlled thyratronrectifier device 'will be abundantly evident to those skilled in the artin the light of the portions of the detailed description which follow.

In FIGURE 1, the response to the various controlled silicon rectifiersand saturable reactors to the successive cycles of supply voltage occursin this manner. When the positive cycle of sine wave voltage is appliedto the contacts C-1 and C-2 (contact C-Z polarized positively withrespect to contact C-l), positive potential is supplied directly to thecenter tap of the primary winding T-1P of transformer T-1. This positivepotential is applied through one-half of the primary winding to theconnection point C and from thence to the anode of the controlledsilicon rectifier CSR-l identified by the arrow symbol. At this time,current is prevented from traversing the controlled silicon rectifierand reaching the connection point A, because the rectifier has not yetbeen gated conductive by the action of the individual control loop whichincludes the saturable reactor SR 1.

During this same half-cycle of positive polarity, the positive voltageexistent at contact 04 is applied via the center tap of primarywindingT-lP to the connection point D on the right-hand side of thebridge, and is thereby simultaneously present at the anode of therectifier CSR-3 identified by the arrow symbol. Once again, currentcannot traverse the rectifier CSR3 and reach the connection point A,because the rectifier has not been gated conductive by potentials withinthe series loop which includes the saturable reactor SR-3.

At any time during this interval of time, the simultaneous gating ofrectifiers CSR-l and CSR-3 to the conductive state will cause current toflow from contact C-2 to the center-tap of the primary winding. Thiscurrent divides and flows in oppositedirections through both halves ofthe tapped primary winding of T-1 to the respective connection points Cand D. From these points, the current flows through the rectifiers CSR-land CSR-3 respectively to the connection point A, and from theconnection point A back through current limiting resistor RO1 to thenegative contact 0-1.

The mechanism of gating the controlled silicon rectifiers to theconductive state in this fashion is as follows: In FIGURE 1, thesecondary winding T-2S has a voltage of predetermined magnitude inducedin itself by the inductive transfer from the primary winding of thetransformer T-2. In the early instants of the time interval underconsideration, the volt-time integral ap-' plied to the gate winding ofsaturable reactor SR-l is not large enough to cause saturation'of SR-land therefore to initiate flow of current in the individual loop whichincludes the diode D-1 and the gate winding of the saturable reactorSR-l. As the amplitude of the positive cycle of supply voltageincreases, the voltage induced into the secondary winding T-ZS willsimilarly increase: When this voltage reaches a critical magnitude whosevalue is determined by the current through the bias wind-. ing of thesaturable reactor SR-l, this reactor becomes saturated and current flowsin the series loop which includes the resistor; R-l, the diode deviceD-1, and the gate electrode of rectifier CSR-l. As soon as this currentflows, the rectifier CSR-l is gated conductive, and current from contactC-2 is able to flow through the lefthand portion of the primary Windingof transformer -T1 to the connection point C, through rectifier CSR-l topoint A, and back to 0-1. This isbecause the element CSR-l after gatingno longer appears as a prac-. tically infinite impedance to the flow ofcurrent.

The mechanism by which the controlled silicon reactor CSR-S is renderedconductive is substantially the same. The rising magnitude of positivevoltage existent in the transformer winding T-2S reaches a criticalpoint'where it is possible to drive current through the saturatedimpedance presented by the gate winding of the saturable reactor SR-3.At this instant, current traverses resistor R-3, the diode D-3, thecontrol electrode of the controlled silicon rectifier CSR-3 and closesupon itself via connection point A.

This mode of firing the silicon rectifiers is somewhat analogous to theoperation ofa grid controlled thyratron tube. With a given value ofbiasing potential on the grid of a thyratron, conduction through thetube is characteristically initiated at a specific point on the AC. sinewave of applied anode'potential. In the bridgetype circuit shown inFIGURE 1, the instant at which the controlled silicon rectifiers fire iscontrolled in a similar fashion. Thus, any of the saturable reactorssuch as the saturable reactor SR-l may be provided with a current in thebias winding which causes the reactor to saturate and present negligibleA.C. impedance at any given instant of the applied alternating voltagewave. When this occurrence takes place, the previous impedance of anelement such as SR-l is reduced to a substantially smaller value. Atthis time, the induced voltage in the secondary winding T-ZS is adequatefor driving current through the resistor R1, the diode D1 and the gateelectrode of the rectifier CSR1, for the purpose .of gating therectifier conductive. By this means, the exact instant of firing respectto the loop of applied sinusoidal-voltage can be determined simply byadjusting the level of the current which flows in the biasing winding ofthe saturable reactor element.

With the background of this explanation, reference will now be made tothe wave form shown in FIGURE 2. This wave form shows the conductionperiods which characterize the quiescent operating level of the powerstage amplifier. voltage in this figure represents the condition whencontact-C-Z is polarized positively with respect to contact C1. As thispositive half-cycle of supply voltage rises and reaches a given point,the controlled silicon rectifier CSR-l is caused to fire as a result ofcurrent flow in the loop which contains the reactor SR-d. An instantlater, the controlled silicon rectifier CSR-3 is caused to experienceconduction Although the firing instants of these two rectifiers inFIGURE 2 have been shown to occur at slightly different instants oftime, for purposes of illustration, both rectifiers would be adjusted bymeans of the bias currents to fire e.g. at exactly 90 on the sine wave.

When this happens, it means that the primary winding of transformer T-1experiences current flow outwardly from the center tap in opposingdirections for equal time intervals. This means that the magnetizingforces which are generated exactly cancel each other, and no energy canbe transferred by induction into the secondary winding for the purposeof energizing the control field of the servomotor 12. In other words,the electrical conduction intervals which occur when reactors SR- l andSR-S are both biased to tire at 90 on the positive cycle have the effectof preventing the application of power to the servomotor 12. This isbecause the supply current enters through contact C2, arrives at thecenter tap of the primary winding, divides exactly in half and flows inopposite directions for equal time intervals in order to reachconduction points Cand D.

these points, the equal halves of the currenttraverse the respectiverectifiers CSR-l and CSR'3 to reunite at the connection point A andreturn as an entity to contact C-1. When the uppermost pair ofcontrolled silicon rectifiers in FIGURE 1 are biased in this manner tofire simultaneously at 90' positive, the ampereturns generated in theprimary winding of the transformer T-l are subtractive and can effectnotransformer action for the purpose of inducing a voltage into thesecondary winding of the transformer T-1. As a result, no current ispresent in the secondary winding of transformer T1 for application tothe control winding of the servomotor12.

When the controlled silicon rectifier CSR-l is biased to fire earlier inthe sine wave than the rectifier CSR-3, the net electrical client ismarkedly different. Current flow then occurs'betwee-n the center tap ofthe primary winding and the connection point C, through the rectifierCS-R-l to the connection point A, and back to contact C-1. At this timethe primary ampereaturns are unopposed by any subtractively polarizedampere turns capable of effecting a net cancellation of all fiux. Afinite interval there-after, the initiation of conduction through therectifier CSR-S permits current flow through the line which includes theopposite half of the tapped primary winding T1P. However, for acontrolled interval, the flux generated within the left-hand portion ofthe primary winding has been allowed to cut the secondary winding T-1Sof transformer T- 1 and induce a voltage therein. As a result, power isapplied to the control field of the servomotor 12 for this finiteinterval. When conduction through CSR-3 is initiated, the resulting fiowof current through the right-hand portion of the tapped primary windinggives rise to a cancellation of primary ampereturns for the remainingportions of the half-cycle. There- The positive half cycle of sine wave8 fore no voltage can exist on the secondary winding of tnansformerT-l.

The conduction periods which occur when the saturable reactor SR-l isgated to permit conduction priorto the commencement of conduction inrectifier -CSR3 are illustrated in FIGURE 3 of the drawings. In thisfigure it will be noted that rectifier OSR-l has been gated conductiveas an example at about 45 electrical degrees, while the rectifier CSR-3remains nonconductive until approximately the point on the positivecycle of the sine wave. By this means, an electrical unbalance in theprimary winding of transformer T-l is caused to occur, and a transfer ofenergy into the secondary winding of the transformer T-l is effected.Returning to the detailed description of FIGURE 1, the conduction pathswhich occur during the negative halfoycle of sine wave supply voltagewill now be explained. The conditions which exist during the quiescentoperating stage will first be set forth. More particularly, when thecontact C-2 becomes negative with respect to contact C1, the conductionpath is as follows. Current enters at contact C-1 and reaches theconnection point B after traversing a current limiting resist-or ll-02.From the connection point B, the current attempts to reach and traverseboth the controlled silicon rectifier CSR-2 in the left-hand portion ofthe drawing and the control-led'rectifier CSR-4 in the right-handportion of the drawing. Conduction through both rectifiers is impossiblehowever, until the appropriate gating signal has been applied to theserectifiers for the purpose of rendering them conductive. Once suchsignal has been applied, the current is of course then capable oftraversing the rectifiers.

In the left-hand portion of the drawing, the path of this current isfrom connection point B through rectifier (ER-2 to connection point C,back through the primary winding of transformer T-1 as far as the centertap, and thence to contact C-2. The other conduction path extends fromconnection point B through rectifier CSR4 to the connection point D;back through the primary winding of transformer T-l as far as the centertap, and thence back to contact C2. 'Once again, during this conductioninterval, the primary winding of transformer T-l experiences a flow ofcurrent in opposite directions from equal time intervals. The flow ofthese currents of identical magnitude in opposite directions results ina subtractive ampere-turns relationship in transformer T-1 whicheffectively prevents the induction of voltage in the secondary of thetransformer during the quiescent operating condition.

It should be appreciated that the symmetrical condition explainedimmediately above is that which occurs when the saturab-le reactorsSR-Zand SR-4 are adjusted by means of the current in their bias windings tosimultaneously fire at e.g. 90 electrical degrees on the negativehalfcycle of sinusoidal supply voltage. is indicated somewhatdiagrammatically in FIGURE 2 for the purposes of illustration. It willbe appreciated that the firing points of OSR-Z and CSR-4 in FIGURE 2would in practice actually coincide at 90 negative.

when the rectifier CSR-2 is biased to fire la predetermined number ofelectrical degrees ahead of the reactor CSR4, a net unbalance of currentin the primary winding of the transformer T-'1 occurs with respect to:time, and the transfer of energy by induction to the control field ofthe servomotor 12 is effected in exactly the same manner as described inconnection with the operation of the rectifiers CSR-l and CSR-3 in theupper portion of FIGURE 1.

Continuing with the detailed description of the invention, reference tothe control signal stage "15 will now be made. The gating of the severalcontrolled silicon rectifiers for conduction at 90, as earlier mentionedrepresents the quiesmnt operating level of the solid-state poweramplifier. In order to cause the servomotor 12 to rotate in either oftwo directions for controlled intervals of time, the firing points ofthe controlled silicon rectifiers CSR-l 9 and CSR-Z may be regulated tocause these rectifiers to fire earlier in time than the reactors CSR-3and CSR-4. This may be repetitively accomplished during each successivehalf-cycle of sine wave voltage by means of the control signal stage 15.Although some control over the firing points of the reactors may beaccomplished by regulating the degree of saturation in the cores by'means of the bias windings, a more sophisticated measure of control overthe firing points is afiorded by the signal stage 15. A current ofpredetermined magnitude and polarity from stage 15 may circulate throughthe several seriesconnected control windings supplied fiom the signalstage 15. With this current the cores of such reactors may be caused tosaturate, time-wise, at a point on the A.C. sine wave which iscontrolled by the value of the current supplied from the signal stage.By this means, moreover, the output current provided by the controlsignal stage 15 is capable of driving the cores of the respectivesaturable reactors into saturation at any predetermined point on theA.C. sine wave. This means that as the magnitude of the potentialinduced in a secondary winding such as T2S is gradually increasing, theeffective impedance of a saturable reactor such as SR-l can be sharplyreduced with attendant gating of the associated rectifier to theconductive state at any point on the alternating current wave. Theinduced voltage in the secondary winding is then immediately capable ofdriving current through the current limiting resistor R-l, the diode D-1and the control electrode for the purpose of gating the rectifier vconductive. If the output voltage from the signal stage 15 is increasedin amplitude, the conduction periods shown in FIGURE 3 expandsymmetrically about the 90 point until at maximum signal the sinusoidalwave shape is finally approached in either positive or negative phase.

If the polarity of the control signal from the signal control stage 15is reversed, then the reactors SR-3 and SR-4 fire earlier in time thanthe reactors SR-l and SR-Z and, correspondingly, the controlled siliconrectifiers CSR-3 and CSR-4 are switched on earlier than the counterpartelements CSR-l and CSR-Z. The result will be a phase reversal of theoutput voltage appearing across the control field winding of theservomotor 12 because of the connection of the center tapped transformerT-1 to the bridge and the supply contacts. This condition of phasereversal is shown in FIGURE 4. The significance of this condition isthat the direction of the torque supplied by the servomotor 12 can bereversed by reversing the polarity of the output voltage produced by thecontrol signal stage 15.

In conclusion, the following summary of the operation of the circuit maybe made. The reactors SR-l and SR-3 in FIGURE 1 may be used to switch onthe controlled silicon rectifiers CSR-l and CSR3 simultaneously at 90firing angle during the positive half-cycle when terminal C-2 ispositive with respect to terminal 0-1. This sets the quiescent operatingpoint for the amplifier. Conversely, the rectifiers CSR-l and CSR-3 arecut olf during the negative half-cycle of supply voltage. The supplyvoltage appears across the resistor RO1 during the positive half-cycleand no induced voltage is produced across the secondary winding oftransformer T1.

During the negative half-cycle when terminal C-l is positive withrespect to terminal C2, the reactors SR-2 and SR-4 act to switch on therectifiers CSR-Z and CSR-4 simultaneously at 90 firing angle. From theforegoing description, it will be recalled that these rectifiers havebeen cut off during the previous positive halfcycle. The supply voltageduring the negative half-cycle appears across current limiting resistorR-O2, and no induced voltage is present across the terminals of thesecondary winding of the transformer T4.

When an A.C. control signal is applied through the control windings forreactors SR-1 through SR4 to fire reactors SR-l and SR-Z earlier in timethan reactors SR-3 and SR-4 during the succeeding half-cycles as 10shown in FIGURE 2, the rectifiers CSR-1 and CSR-2 conduct earlier intime than the rectifiers CSR3 and CSR-4, to permit energy transfer by.induction to the output terminals of transformer T-1.

During the time which elapses between the switching on of rectifiersCSR-l and CSR-3 and the respective rectifiers CSR-2 and CSR-4, theoutput voltage which appears across the windings of the transformer T-1effects this transfer of energy to the control field of the servomotor12. As earlier explained in this specification, this condition isillustrated in FIGURE 3 by hatched areas which represent the inducedvoltage available at the output terminals of transformer T1. The outputvoltage derived by reversing the polarity of the signal from the controlsignal stage 15 is illustrated by the hatched areas shown in FIGURE 4 ofthe accompanying drawings.

The amplifier circuit invention produces currents in a center tappedwinding T] P that result in magnetic fields having an average amplitudeand a phase relationship which are respectively dependent upon the inputsignal amplitude and polarity. The transformer T-1 of the embodiment ofFIGURE 1 efficiently couples the output to the servo motor 12. However,the center tapped output winding T 1P or its equivalent can be employedfor any useful purpose, and the output winding can also be a centertapped control phase of a motor.

There has been described one embodiment of a newly developed power stageamplifier incorporating controlled silicon rectifiers used inconjunction with half-cycle response magnetic amplifiers and a centertapped output transformer for the purpose of producing an output signalI of predetermined polarity and magnitude. Although the use of suchsignals in driving a reversible servomotor has been explained incompleting the detailed description of the invention, it will beappreciated that this type of signal may be used for many otherapplications which require potential of variable magnitude and polarity,and that such use of the circuitry would fall squarely within the spiritand scope of the appended claims.

What I claim is:

1. In a solid-state power stage amplifier circuit for producing anoutput signal of controllable magnitude and polarity, contact meansconnected to receive power from a source of alternating voltage, bridgecircuit means including two pairs of oppositely poled rectifiersconnected to define a set of four individual connection pointstherebetween, a transformer provided with a primary winding having acenter tap contact, a first group of conductors connected to couple saidcenter tap contact to one of said contact means and the opposite ends ofsaid primary winding to a first pair of said individual connectionpoints, a second group of conductors connected to couple the other ofsaid contact means to a second pair of said connection points, and meansincluding saturable reactor means connected each to sample saidalternating voltage and initiate conduction through each of saidrectifiers at a predetermined instant during the successive half-cyclesof said voltage.

2. In a solid-state power stage amplifier circuit for producing anoutput signal of predetermined magnitude and polarity, contact meansconnected to receive power from a source of alternating voltage; a firstpair of similarly poled normally noneonductive rectifiers coupled inseries with a first connection point therebetween, a second pair ofsimilarly poled normally nonconductive rectifiers coupled in series witha second connection point therebetween, said first and second pairs ofrectifiers coupled together to provide third and fourth connectionpoints therebetween; a transformer provided with a center tapped primarywinding and means coupling the opposite ends of said winding across saidfirst and second connection points respectively, first conductor meanscoupling one of said contact means to the center tap of said primarywinding, second conductor means coupling the other of said contact meansto said third and fourth connection points, and means includingsaturable reactor means connected to render each of said rectifiersconductive at a predetermined instant during the successive halfcyclesof said alternating voltage.

3. In a solid-state power stage amplifier circuit for a second pairofsimilarly poled normally nonconductive rectifiers coupled in series witha second connection point therebetween, said first and second pairs ofrectifiers coupled together to provide third and fourth connectionpoints therebetween, each of said rectifiers provided with a controlelectrode for receiving a voltage impulse to render said rectifierconductive; a transformer provided with a center tapped primary windingand means coupling opposite ends of said winding across said first andsecond connection points respectively, first conductor means couplingone of said contact means to the center tap of said primary winding,second conductor means coupling the other of said contact means to saidthird and fourth connection points, and means including diode means andsaturable reactor means connected in-circuit with each of said controlelectrodes for said rectifiers for rendering said rectifiers conductiveat a predetermined instant during the successive half-cycle of saidalternating voltage.

4. In a solid-state power stage amplifier circuit for producing anoutput signal of predetermined magnitude and polarity, contact meansconnected to receive power from a source of alternating voltage; a firstpair of similarly poled normally nonconductive rectifiers coupled inseries with a first connection point therebetween, a second pair ofsimilarly poled normally nonconductive rectifiers coupled in series witha second connection point therebetween, said first and second pairs ofrectifiers coupled together to provide third and fourth connectionpoints therebetween, each of said rectifiers provided with a controlelectrode for receiving a voltage impulse to render said rectifierconductive; a transformer provided with a center tapped primary windingand means coupling opposite ends of said winding across said first andsecond connection points respectively, first conductor means couplingone of said contact means to the center tap of said primary winding,second conductor means coupling the other of said contact means to saidthird and fourth connection'points, a second transformer connected tosample said alternating voltage and induce potential within a pluralityof individual secondary windings, and means including diode means and asaturable reactor connected in circuit between each of said controlelectrodes and opposite ends of one of said secondary windings forrendering said rectifiers conductive at a predetermined instant duringthe successive half-cycles of said alternating voltage.

5. In a solid-state power stage amplifier circuit for producing anoutput signal of predetermined magnitude and polarity, contact meansconnected to receive power from a source of alternating voltage; bridgecircuit means including two pairs of oppositely poled rectifiersconnected to define a set of four individual connection pointstherehetween, each of said rectifiers provided with a control electrodefor receiving gating potential to initiate conduction therethrough; atransformer provided with a primary winding having a center tap contact,a first group of conductors connected to couple said center tap contactto one of said contact means and the opposite ends of said primarywinding to a pair of said individual connection points, a second groupof conductors connected to couple the other of said contact means to asecond pair of said connection points, and means including saturablereactor means connected each to sample said alternating voltage andapply gating potential to said g 12 control electrodes to initiateconduction through said rectifiers at predetermined instants during thesuccessive half-cycles or said alternating voltage.

6. In a solid-state power stage amplifier circuit for producing anoutput signal of predetermined magnitude and polarity, contact meansconnected to receive power from a source of alternating voltage, bridgecircuit means including two pairs of oppositely poled rectifiersconnected to define a set of four individual connection pointstherehetween, a transformer provided with a primary winding having acenter tap contact, a first group of conductors connected to couple saidcenter tapcontact to one of said contact means and the opposite ends ofsaid primary Winding to a pair of said individual connection points, asecond group of conductors connected to couple the other of said contactmeans to a second pair of said connection points, and means includingdiode means and a plurality of individual saturable reactor means eachhaving a gate winding connected to selectively apply gatingpotential toone of said rectifiers at a predetermined instant during the successivehalf-cycles of said alternating voltage to initiate conductiontherethrough.

7. In a solid-state power stage amplifier circuit for producing anoutput signal of predetermined magnitude and polarity, contact meansconnected to receive power from a source of alternating voltage, bridgecircuit means including two pairs of oppositely poled rectifiersconnected to define a set of four individual connection pointstherebetween, a transformer provided with a primary winding having acenter tap contact, a first group of conductors connected to couple saidcenter tap contact to one of said contact meansand the opposite ends ofsaid primary winding to a pair of said individual connection points, asecond group of conductors connected to couple the other of said contactmeans to a second pair of said connection points, means including diodemeans and a plurality of individual saturaole reactor means each'havinga gate winding connected to selectively apply gating potential to one ofsaid rectifiers at a predetermined instant during the successivehalf-cycles of said alternating voltage to initiate conductiontherethrough, and means including a signalcontrol stage connected tosupply current of predetermined amplitude and polarity to the controlwindings of each of said individual saturable reactor means to fix saidpredetermined instant at which said conduction through said rectifiersis initiated.

8. In a solid state power amplifier circuit for producing an outputsignal of controllable magnitude and polarity, a source of alternatingvoltage, bridge circuit means including four silicon controlledrectifiers each having a cathode, an anode and gate electrode, a firstconnection point represented by the cathode electrodes of two of saidrectifiers connected in common, a second connection point formed by theanode electrodes of two of the other of said rectifiers connected incommon, third and fourth connection points being the remaining commonconnections between the anode and cathode electrodes, a transformerhaving a primary winding with a center tap contact, said center tapcontact being connected to one side of said source of alternatingvoltage, the ends of said primary winding being connected to said thirdand fourth connection points, said first and second connec tion pointseach resistively connected to said source of alternating voltage, andmeans including diodes and saturable reactors connected to each gateelectrode of said controlled rectifiers, each of said last named meansbeing for sampling said alternating voltage and initiating conductionthrough each of said controlled rectifiers at a predetermined instantduring successive half-cycles of said volage.

9. In a solid-state power stage amplifier circuit for producing anoutput signal of controllable magnitude and polarity, contact meansconnected to receive power from a source of alternating voltage, bridgecircuit means including two pairs of oppositely poled rectifiersconnected to define a set of four individual connection pointstherebetween, output inductance means including a winding having acenter contact, a first group of conductors connected to couple saidcenter contact to one of said contact means and the opposite ends ofsaid winding to a first pair of said individual connection points, asecond group of conductors connected to couple the other of said contactmeans to a second pair of said connection points, and means includingsaturable reactor means connected each to sample said alternatingvoltage and initiate conduction through each of said rectifiers at apredetermined instant during the successive half-cycles of said voltage.

10. In a solid-state power stage amplifier circuit for producing anoutput signal of predetermined magnitude and polarity, contact meansconnected to receive power from a source of alternative voltage; a firstpair of similarly poled normally nonconductive rectifiers coupled inseries with a first connection point therebetween, a second pair ofsimilarly poled normally nonconductive rectifiers coupled in series witha second connection point therebetween, said first and second pairs ofrectifiers coupled together to provide third and fourth connectionpoints therebetween; output inductance means including a winding havinga center contact, and means coupling the opposite ends of said windingacross said first and second connection points respectively, firstconductor means coupling one of said contact means to the center of saidwinding, second conductor means coupling the other of said contact meansto said third and forth connection: points, and means includingsaturable reactor means connected to render each of said rectifiersconductive at a predetermined instant during the successive half-cyclesof said alternative voltage.

11. In a solid-state power stage amplifier circuit for producing anoutput signal of predetermined magnitude and polarity, contact meansconnected to receive power from a source of alternating voltage, bridgecircuit means including two pairs of oppositely poled rectifiersconnected to define a set of four individual connection pointstherebetween, output inductance means including a winding having acenter contact, a first group of conductors connected to couple saidcenter contact to one of said con tact means and the opposite ends ofsaid winding to a pair of said individual connection points, a secondgroup of conductors connected to couple the other of said contact meansto a second pair of said connection points, means including diode meansand a plurality of individual saturable reactor means each having a gatewinding connected to selectively apply gating potential to one of saidrectifiers at a predetermined instant during the successive half-cyclesof said alternating voltage to initiate conduction therethrough, andmeans including a signal control stage connected to supply current ofpredetermined amplitude and polarity to the control windings of each ofsaid individual saturable reactor means to fix said predeterminedinstant at which said conduction through said rectifiers is initiated.

12. In a solid state power amplifier circuit for producing an outputsignal of controllable magnitude and polarity, a source of alternatingvoltage, bridge circuit means including four silicon controlledrectifiers each having a cathode, an anode and gate electrode, a firstconnection point represented by the cathode electrodes of two of saidrectifiers connected in common, a second connection point formed by theanode electrodes of two of the other of said rectifiers connected in.common, third and fourth connection points being the remaining commonconnections between the anode and cathode electrodes, output inductancemeans including a winding having a center contact, said center contactbeing connected to one side of said source of alternating voltage, theends of said winding being connected to said third and fourth connectionpoints, said first and second connection points each resistivelyconnected to said source of alternating voltage, and means includingdiodes and saturable reactors connected to each gate electrode of saidcontrolled rectifiers, each of said last named means being for samplingsaid alternating voltage and initiating conduction through each of saidcontrolled rectifiers at a predetermined instant during successivehalf-cycles of said voltage.

References Cited in the file of this patent or the original patentUNITED STATES PATENTS McGraW-Hill Co., Inc., 1st edition, page 149, FIG.10.2 and page 205, FIG. 14.31).

Solid-State Thyratron Switches Kilowatts by Frenzel and Gutzwiller,Electronics, Mar. 28, 1958.

Notes on the Application of the Silicon Controlled Rectifier (EGG-3714),December 1959.

